1. Field of the Invention
The present invention relates to a process and an installation for producing boards of wood-based material.
In particular, the present invention concerns the optional production of structured surfaces on boards of wood-based material--preferably OSB (oriented stranded boards) boards--which are produced by single platen or multi-platen presses or by continuously operating presses.
2. Description of Related Art
It is known to structure one side of OSB boards for achieving better adhesion properties in the case of roof sheeting used in prefabricated house construction. In this case, OSB boards with structuring on one side are produced on single platen or multi-platen presses by scattering chippings onto metal mesh mats or perforated transporting plates. The metal mesh mats correspond to the geometric size of the respective pressing/heating platen of the single or multi-platen press. In the case of single platen or multi-platen systems, a metal mesh belt or perforated transporting plate has two functions: first, the metal mesh belt is used to transport the pressed stock to a respective level between the pressing/heating platen(s) of the press and also to remove it again as a finished board of wood-based material, and second, the mesh structure of this metal mesh belt (transporting mat) is used for producing the structuring on the surface of the OSB board during the pressing operation. The later being accomplished by making use of the plasticity of the heated wood-based material which occurs automatically due to the vaporization in the press of the moisture introduced with the pressed stock.
Surface structuring for boards of wood-based material is also known with a continuously operating press according to German Patent No. 43 33 614. A metal mesh belt is made to circulate around the lower pressing/heating platen and, as in the case of the application in platen presses, is used as a transporting and structuring belt. This patent is primarily directed to the advantages of a preheating zone, however, structuring of the board of wood-based material is also produced during the continuous pressing operation. The plasticity of the board of wood-based material caused during the pressing operation being made use of in the same way as discussed above with regard to single platen or multi-platen presses.
Disadvantages of both press arrangements arise due to the combination of the two functions: transporting and simultaneous structuring.
Optional pressing with smooth surfaces on both sides is possible only with considerable effort by changing over the charging devices. In the case of single platen or multi-platen presses, smooth plates have to be exchanged for the metal mesh belts. In the case of a continuously operating press, the endlessly circulating metal mesh belt would have to be replaced with by a smooth belt, or entirely eliminated such that transfer of the pressed stock directly into the press would be performed by the transfer belts. For these reasons, such change-overs cannot be carried out cost-effectively. Further, this negatively affects contemporary "just-in-time" production processes due to the long inactive times between producing boards of wood-based material with a smooth surface and with structuring on one or both sides.
An alternative solution is to subsequently structure finished, cooled-down boards of wood-based material. However, this leads to reductions in the flexural strength of the board and the adhesiveness on these structured surfaces.